Tumor cell targeting with Escherichia coli displaying anti-EGFR antibody fragments

Weckenbrock W, Blaßhofer F, Klotz LO, Jose J

Abstract

Bacterial tumor cell targeting describes the use of selective affinity of bacterial cells towards tumorous tissue for cancer diagnosis or treatment [1]. The oral or rectal application of bacteria is possible, because lipopolysaccharide (LPS) induced toxicity only applies for systemic use. Therefore, in gastrointestinal cancer, bacteria with distinct affinity for malignant cells could serve as drug carriers delivering a drug precisely to the spot of interest. In case of peptidic drugs, the bacterial cell could serve as both the carrier and the producing unit. The design of tumor targeting bacteria which express a prodrug converting enzyme is also an interesting idea. Thus, a prodrug could be converted into the active agent selectively within malignant tissue. The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase [2]. EGFR is the target of several drugs, including both small molecule (e.g. gefitinib or erlotinib) and monoclonal antibodies (cetuximab or panitumumab), because the overexpression of EGFR is associated with colorectal tumors and other sorts of cancer [3]. Due to its location on the tumors cell surface EGFR is a suitable target for bacterial drug targeting. The aim of this study was to design a strain of E.coli with distinct affinity towards EGFR. For this purpose, anti-EGFR single chain variable fragment (scFv) 425 [4] was displayed on the surface of E.coli using the AIDA-I-autotransporter technology [5]. The affinity of E.coli cells displaying the antibody fragment towards tumor cells overexpressing EGFR was demonstrated in FACS and fluorescence microscopic assays. Specificity of binding to the EGF-receptor was proven in experiments using siRNA down-regulation of this receptor. Our findings demonstrate that E.coli displaying antibody fragments can be used for tumor cell targeting in vitro. Further experiments on the applicability of this technology in vivo are needed.